Interaction of a water molecule with the oxygen vacancy on the MgO(100) surface - art. no. 125426

The interaction of a water molecule with a neutral oxygen vacancy on the Mg O(100) surface is studied in the limit of very low coverage by total-energy calculations and molecular-dynamics simulations based on the density-funct ional theory. Exchange and correlation effects are treated within the gener alized gradient approximation. We show the existence of a local minimum cor responding to the physisorbed adsorption state, which is similar to the one found for water adsorption on the stoichiometric MgO(100) surface. At vari ance with the latter one, the dissociation of the water molecule is energet ically favored at the vacancy site. However, the global energy minimum corr esponds to the recombined configuration, in which the oxygen initially in t he water molecule adsorbs in the vacancy and the two hydrogens form a HZ di mer. Through the evaluation of the energy barriers between the different st ates we discuss the kinetics of the interaction of the water molecule with the defective surface. We show that the dissociated configuration is likely only an intermediate state towards the recovery of a stoichiometric surfac e, thus suggesting that dissociation of an isolated water molecule at the n eutral oxygen vacancy cannot be held as responsible for the existence of a stable hydroxyl group on the MgO(100) surface.